Sort libsodium sources by path in sys/modules/crypto/Makefile.

This matches the order used in sys/conf/files to make it easier to
keep these two files in sync.

Reviewed by: imp
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D33484

(cherry picked from commit 8b4af206f67e93735a5b22921469a2bce63fb6ab)